Epoxy resin-cured products are used in a variety of fields such as insulating materials, adhesives, and paints due to their superiority in electrical characteristics, heat resistance, and adhesion. However, since the epoxy resin becomes infusible and insoluble in general-purpose solvents after it is thermo-cured, it has been difficult to recycle the epoxy resin-cured products and products to which the epoxy resin-cured product adheres or on which the epoxy resin-cured product is applied. Furthermore, it has been difficult as well to separate inorganic fillers, inorganic fibers, inorganic textile fabrics, inorganic fiber nonwoven fabrics, etc., which are blended with the epoxy resin to increase the resin's mechanical properties or the like, from the resin-cured products, for recycling purpose.
A technique of grinding, pulverizing, and separating according to specific gravity is a known example of a method of separating a printed wiring board, which is a composite material of epoxy resin-cured product and inorganic matter such as glass fiber and metal, into each component. However, although recovery and recycling of metals are possible to some extent in this method, pulverized glass fibers and resin powders thus obtained can be utilized only as fillers. Therefore their value as valuable goods is significantly low, and, in addition, it has been impossible to separate each component perfectly. Also, known examples include a method in which resins of printed wiring boards, laminates or the like are thermal-decomposed to recover metals and glass fibers while the thermal-decomposed resins are gasified or liquidized for the recovery, and a method of recovering not only inorganic matter but also the thermal decomposed resins. However, these methods have several problems as follows. Thermal decomposition of resins requires high temperatures so that obtained metals and inorganic matter are oxidized and denaturalized while resins are oxidized or carbonized, thereby decreasing their value; when resins contain toxic materials such as halogens and lead, separation and treatment of these materials require enormous costs.
As mentioned above, for the purpose of recycling of resins, thermal decomposition of resins is not generally preferred. For this reason, there has been a proposition for a method of dissolving thermosetting resin-cured wastes in solvents, especially in organic solvents to separate inorganic matter such as metal and glass (see Japanese Unexamined Patent Application Publication No. 10-314713).
However, because thermosetting resins including the epoxy resin are generally poorly soluble in general-purpose solvents as is clear from their definition “resin rendered insoluble and infusible by application of heat”, general solvents as exemplified in the above publication do not have enough solvency for separation and recovery of resin-cured products. Therefore, pulverization is required as a pretreatment before the dissolving treatment, which places a limitation on the recycling application of recovered inorganic matter such as glass fibers in that recovered inorganic matter can be utilized only as pulverized matter and not as woven or nonwoven fabric without reprocessing.